The present invention relates to an active matrix display device and an inspection method for the same, more particularly to an active matrix display device having an inspection circuit for the display device and an inspection method for the same.
The manufacturing process for a thin film transistor (TFT) color liquid crystal display device which has been widespread today can be roundly separated into a manufacturing process for a liquid crystal (LC) cell, a manufacturing process for an LC module and a manufacturing process for an LC monitor. The LC module is completed by connecting, to the LC cell, a driver IC and a drive circuit which generates control signals to be inputted to the driver IC, and attaching a back light and mechanical components. Further, the LC monitor is completed by connecting a graphics adapter, which generates signals including image information to be inputted, to this LC module, and attaching mechanical components.
In the manufacturing of LC display devices, it is necessary to find defects, at an early stage, originated from dust entered or a dimensional error occurred in the manufacturing process in order to improve the manufacturing efficiency. In this respect, various tests, such as a gap test and a lighting test, are conducted in the respective stages of the manufacturing process for the LC display devices.
For example, Japanese Patent Laid-Open No. Sho 60-2989 discloses a method of detecting disconnection and short-circuiting of data/scan lines of a TFT array. With this method, disconnection of data/scan lines can be detected in an LC display device having only one X drive circuit. Disconnection and short-circuiting of the data/scan lines are detected by providing test transistors on the opposite side to the X drive circuit. Specifically, a specific test signal inputted from the drive circuit is outputted from the test transistors to carry out the inspection.
Further, Japanese Patent Laid-Open Nos. Hei 3-18891, 3-20721, 5-5897 and 5-11000 disclose schemes of inspecting an active matrix array by connecting signal lines or switching circuits for inspection to the active matrix array on the opposite side to the drive circuit.
Japanese Patent Laid-Open No. Hei 2-154292 describes a disconnection test on an active matrix array before connecting a driver IC to the array by using a selector circuit which has an analog switching function.
One of these inspection techniques is an image quality inspection which is performed after a TFT LC cell is completed. There are various ways to inspect the image quality of a TFT LC cell, and a typical inspection scheme is a multiple pin probe method.
According to this method, in the last step of manufacturing an LC cell, multiple pin probes independently contact all the signal input terminals of the LC cell to input electrical signals equal to input signals from a driver IC in an LC module. This method can completely recreate the driving of an LC cell as a final product, hence, the inspection can be carried out by visually checking the display screen of the final product. In this case, adequately preparing the input signals can permit every kind of screen to be displayed. However, the inspection with the multiple pin probe system has the following problems.
First, multiple pin probes are expensive and need a significant time for its fabrication. For an LC cell having 1024 pixels (xc3x973 sub pixels)xc3x97768 rows, for example, there should be at least 3840 signal input lines, hence, inspection of the image quality requires probes which can contact nearly 4000 signal input terminals.
There is also a matter of inspection stability. In accordance with the recent trend of larger and higher definition LC cells, the probe portions increase and their density becomes higher, hence, one should consider unstable electric contact of the probes. When electric contact becomes unstable, a signal to be inputted does not travel through some signal input lines and a test screen associated with such lines will not be displayed. This considerably reduces the inspection efficiency. This is fatal in the case of performing automatic inspection by means of image processing. Further, since an improvement on the high definition of an LC cell narrows the gap between the probes adjacent to each other, there is a certain limit to the preparation of such probes, not to mention the reduction in inspection reliability.
In addition, such multiple pin probes cannot be adapted to multi-production, thus resulting in a higher cost and a lower inspection efficiency. This is because for multi-production of LC cells, it is difficult to provide a common layout for probes between different types of products due to the difference in specifications of the individual types of products and it is necessary to prepare probe sets product by product and change one probe set mounted to the inspection apparatus to another product set.
In view of the above, there is a demand for an inspection method which does not require the multiple pin probes even if the kinds of test screens to be displayed are limited.
A feature of the present invention is to provide a display device and an inspection method for the same, which are capable of efficiently inspecting the image quality.
Another feature of the present invention is to provide a display device having an inspection circuit that can cope with multiple image quality inspections, and an inspection method for the same.
A further feature of the present invention is to provide a display device and an inspection method for the same, which are capable of reliably self inspection.
It is a still further feature of the present invention to provide an apparatus and an inspection method for the same, which are capable of reliably inspection of a large and high-definition display device.
It is a yet further feature of the present invention to provide a display device and an inspection method for the display device, which are capable of efficiently inspecting the image quality prior to the attachment of a driver IC to the display device.
An active matrix display device according to the present invention has an inspection circuit for inspecting the image quality. This inspection circuit includes a plurality of input terminals for inputting a test signal and a plurality of test transistors connected respectively to the input terminals. Input test signals which are to be sent to sub pixel sections from the individual input terminals are controlled by the associated test transistors to display a desired test screen. The test transistors are preferably amorphous silicon TFTs.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings.